http://revach.net/article.php?id=3410

Section: Halacha   Category: Tshuvos
Rav Moshe Shternbuch: Is It Preferable to Speak Ivrit Over English?
RavMoshe Shternbuch (1:538) quotes the Rambam who says that the language is not important, only the content.  Nevertheless says Rav Shternbuch, to the extent that the language you speak will impact the content you discuss, it does become an issue. 

Therefore if when speaking Lashon Kodesh you will not speak Lashon Hara and other forbidden things like leitzanus and lies, then surely it is better to speak Lashon Kodesh.  If however you will speak these things even in Lashon Kodesh,then he says it is better not to defile the holy language with improper speech and you are better off speaking a different language.

However he makes a distinction between Lashon Kodesh and "Ivrit".  Ivrit he says, is worse than other languages because it was created by people who have no part of the Torah and all their intentions were purely nationalistic.  Certainly there is no kedusha in this language.  He adds that when the non-religious element started speaking Ivrit in Yerushalayim, Rav Yehoshua Leib Diskin decided that the people in Yerushalayim should switch over to speaking Yiddish as opposed to Lashon HaKodesh, which was too similar to the national language of Ivrit.

Important Note: We try to convey the Tshuva to the best of ourability. We admit that our understanding may not be accurate. One should learn the tshuva to verify the accuracy of our interpretation.  Please also understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.